[PATCHv3] inotify: Convert to using per-namespace limits

Nikolay Borisov n.borisov.lkml at gmail.com
Thu Dec 15 07:26:22 UTC 2016



On 15.12.2016 02:37, Eric W. Biederman wrote:
> Nikolay Borisov <n.borisov.lkml at gmail.com> writes:
> 
>> This patchset converts inotify to using the newly introduced
>> per-userns sysctl infrastructure.
>>
>> Currently the inotify instances/watches are being accounted in the
>> user_struct structure. This means that in setups where multiple
>> users in unprivileged containers map to the same underlying
>> real user (i.e. pointing to the same user_struct) the inotify limits
>> are going to be shared as well, allowing one user(or application) to exhaust
>> all others limits.
>>
>> Fix this by switching the inotify sysctls to using the
>> per-namespace/per-user limits. This will allow the server admin to
>> set sensible global limits, which can further be tuned inside every
>> individual user namespace. Additionally, in order to preserve the
>> sysctl ABI make the existing inotify instances/watches sysctls
>> modify the values of the initial user namespace.
>>
>> Signed-off-by: Nikolay Borisov <n.borisov.lkml at gmail.com>
>> Acked-by: Jan Kara <jack at suse.cz>
>> Acked-by: Serge Hallyn <serge at hallyn.com>
>> ---
>>
>> Okay, so here is another version, which should 
>> hopefully be free of slab corruptions. There was an issue
>> where in ucount.c the ifdef was checking the CONFIG_INOTIFY_USER_
>> (pay attention to the trailing _, this was clearly a mistake). This 
>> led to the user_table (and all duplicated from it tables) to not 
>> contain the inotify-related members. In my local testing I got 
>> kasan splats even during kernel boot, due to out-of-bound writes. 
>> Let's see how this version fares.
> 
> So there is one more thing that needs to be addressed with your patch.
> 
> In inotify.h the functions need to be marked static inline
> rather than just static or else there a number of new compiler warnings.
> 
> I have addressed this for now, but if anything else comes up or if you
> resend this patch I would appreciate it if you add the static inline
> notations in your internal copy of the patch.

Okay, I will keep this in mind. Btw, do you compile with W=1 to get
those warnings, since I don't get them when I just run plain make?


> 
> Thank you,
> Eric Biederman
> 
> 
>> diff --git a/fs/notify/inotify/inotify.h b/fs/notify/inotify/inotify.h
>> index ed855ef6f077..b5536f8ad3e0 100644
>> --- a/fs/notify/inotify/inotify.h
>> +++ b/fs/notify/inotify/inotify.h
>> @@ -30,3 +30,20 @@ extern int inotify_handle_event(struct fsnotify_group *group,
>>  				const unsigned char *file_name, u32 cookie);
>>  
>>  extern const struct fsnotify_ops inotify_fsnotify_ops;
>> +
>> +#ifdef CONFIG_INOTIFY_USER
>> +static void dec_inotify_instances(struct ucounts *ucounts)
>> +{
>> +	dec_ucount(ucounts, UCOUNT_INOTIFY_INSTANCES);
>> +}
>> +
>> +static struct ucounts *inc_inotify_watches(struct ucounts *ucounts)
>> +{
>> +	return inc_ucount(ucounts->ns, ucounts->uid, UCOUNT_INOTIFY_WATCHES);
>> +}
>> +
>> +static void dec_inotify_watches(struct ucounts *ucounts)
>> +{
>> +	dec_ucount(ucounts, UCOUNT_INOTIFY_WATCHES);
>> +}
>> +#endif


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